1. Field of the Invention
The present invention generally relates to treatment of spent, or used, dryfilm photoresist and solder mask stripping and developing solutions used in the printed circuitry industry.
2. Background of the Invention
Over the past thirty years the printed circuit industry has undergone substantial increases in the volume of printed circuit boards being made and also the volume of chemicals used in the fabrication of those boards. The treatment of the waste materials produced by this industry has not kept pace with the technical advances made in the production of those boards. These waste materials are dangerous and costly to treat and the need to improve the treatment of these waste materials is becoming more critical.
An article in the industry magazine "Printed Circuit Fabrication", volume 10, No. 5, May, 1987 by Mr. Peter R. Rose entitled "Dryfilm Resist Stripping" starting on page 55 details techniques for using strippers. On page 58 at the bottom of column 2 and the top of column 3, the hazards of spent strippers are listed. These hazards include heavy metals, polymers, and the high alkaline content of these spent strippers. Mr. Rose, in the same section, mentions a proprietary process which aids by removing polymers by precipitation. This may be the process described in a brochure by Inland Specialty Chemical Co. of 3151 Airway Avenue, J-3, Costa Mesa, Calif. 92626 as "Novatreat".
"Novatreat" purports to prevent the forming of a sticky residue during the treating of spent strippers. However, as described in the last paragraph, the "Novatreat" is added "slowly and carefully to the cooled solution"; this infers that the hazards to the operators and the environment due to heat and fumes continues to exist.
Typical state of the art treatment of waste strippers is outlined in the brochure from J&S Laboratories Inc., 521 East "D" st., Wilmington, Calif. 90744. The treatment calls for the addition of 25% sulfuric acid solution to the spent stripper material, which is highly alkaline, in an open vessel. This process produces a precipitate and a violent reaction with heat and fumes which are dangerous to the operators and the local environment. pH is monitored to determine when this part of the process is complete, but this is not reliable since the precipitate is sticky and interferes with the pH measuring probe. The precipitate is removed by filtration, which is also adversely affected by the sticky precipitate, and the remaining fluid is fed to another treatment facility. However, the fluid, called supernatant, still contains dissolved stripper, lead, tin, copper and their compounds, since the treatment is not necessarily complete. This entire process takes more than two hours.
The supernatant is fed through chelated rinses, but the supernatant interferes with sludge formation, which does not easily settle and constantly clogs the system.
Consequently there is a need for a faster and more economical treatment, where the material is more completely treated, where the solid residue is benign, non-sticky and more easily removed by filtration, and where the residual supernatant is easily treated in typical chelated rinses without clogging. Additionally a need exists for a treatment where there is no violent reaction, with negligible heat and fumes, which will be safer for the operator and the environment.